The geochemistry of alkali metal ions in the Wairakei hydrothermal system

Abstract

Chemical analyses show that in the Wairakei hydrothermal field hot chloride water is fed to the levels tapped by the drillholes by at least two separate entries — one near the group of holes in the East, and another West of, or about, the main Western production group. This is in agreement with the results of physical measurements of temperature and pressure in the area. The changes in concentrations of the various alkali metal ions in the waters can be correlated with their reaction with country rock to form the various zones of hydrothermal alteration found by petrological examination of drill cores. The chemical results ar,e sufficient to show that all the Wairakei waters are of a common primary origin. The high concentration in the waters of the rare element caesium is evidence that the source of the dissolved chemicals is a high temperature and pressure magmatic steam phase. The constancy of the chemical characteristics over a period of seven years indicates that the hold-up volume in the Wairakei circulatory system must be large compared with the present total volume drawn from the area by drillholes.